@article {KNZ001983, title = {Shifts in plant functional composition following long-term drought in grasslands}, journal = {Journal of Ecology}, volume = {107}, year = {2019}, pages = {2133 - 2148}, abstract = {

\ 1. Plant traits can provide unique insights into plant performance at the community scale. Functional composition, defined by both functional diversity and community-weighted trait means (CWMs), can affect the stability of above-ground net primary production (ANPP) in response to climate extremes. Further complexity arises, however, when functional composition itself responds to environmental change. The duration of climate extremes, such as drought, is expected to increase with rising global temperatures; thus, understanding the impacts of long-term drought on functional composition and the corresponding effect that has on ecosystem function could improve predictions of ecosystem sensitivity to climate change.
\ 2. We experimentally reduced growing season precipitation by 66\% across six temperate grasslands for 4 years and measured changes in three indices of functional diversity (functional dispersion, richness and evenness), community-weighted trait means and phylogenetic diversity (PD). Specific leaf area (SLA), leaf nitrogen content (LNC) and (at most sites) leaf turgor loss point (πTLP) were measured for species cumulatively representing ~90\% plant cover at each site.
\ 3. Long-term drought led to increased community functional dispersion in three sites, with negligible effects on the remaining sites. Species re-ordering following the mortality/senescence of dominant species was the main driver of increased functional dispersion. The response of functional diversity was not consistently matched by changes in phylogenetic diversity. Community-level drought strategies (assessed as CWMs) largely shifted from drought tolerance to drought avoidance and/or escape strategies, as evidenced by higher community-weighted πTLP, SLA and LNC. Lastly, ecosystem drought sensitivity (i.e. relative reduction in ANPP in drought plots) was positively correlated with community-weighted SLA and negatively correlated with functional diversity.
\ 4. Synthesis. Increased functional diversity following long-term drought may stabilize ecosystem functioning in response to future drought. However, shifts in community-scale drought strategies may increase ecosystem drought sensitivity, depending on the nature and timing of drought. Thus, our results highlight the importance of considering both functional diversity and abundance-weighted traits means of plant communities as their collective effect may either stabilize or enhance ecosystem sensitivity to drought.

}, keywords = {LTER-KNZ, ANPP, Climate change, community weighted traits, Drought, Functional diversity, plant functional traits}, doi = {10.1111/1365-2745.13252}, url = {https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.13252}, author = {Griffin-Nolan, Robert J. and D.M. Blumenthal and Scott. L. Collins and Farkas, Timothy E. and Hoffman, Ava M. and Mueller, Kevin E. and Ocheltree, Troy W. and M.D. Smith and Whitney, Kenneth D. and Alan K. Knapp}, editor = {Jones, Holly} } @article {KNZ001883, title = {Trait selection and community weighting are key to understanding ecosystem responses to changing precipitation regimes}, journal = {Functional Ecology}, volume = {32}, year = {2018}, pages = {1746 - 1756}, abstract = {

1. Plant traits can be used to predict ecosystem responses to environmental change using a response\–effect trait framework. To do this, appropriate traits must be identified that explain a species\&$\#$39; influence on ecosystem function (\“effect traits\”) and the response of those species to environmental change (\“response traits\”). Response traits are often identified and measured along gradients in plant resources, such as water availability; however, precipitation explains very little variation in most plant traits globally. Given the strong relationship between plant traits and ecosystem functions, such as net primary productivity (NPP), and between NPP and precipitation, the lack of correlation between precipitation and plant traits is surprising.

2. We address this issue through a systematic review of \>500 published studies that describe plant trait responses to altered water availability. The overarching goal of this review was to identify potential causes for the weak relationship between commonly measured plant traits and water availability so that we may identify more appropriate \“response traits.\”

3. We attribute weak trait\–precipitation relationships to an improper selection of traits (e.g., nonhydraulic traits) and a lack of trait-based approaches that adjust for trait variation within communities (only 4\% of studies measure community-weighted traits). We then highlight the mechanistic value of hydraulic traits as more appropriate \“response traits\” with regard to precipitation, which should be included in future community-scale trait surveys.

4. Trait-based ecology has the potential to improve predictions of ecosystem responses to predicted changes in precipitation; however, this predictive power depends heavily on the identification of reliable response and effect traits. To this end, trait surveys could be improved by a selection of traits that reflect physiological functions directly related to water availability with traits weighted by species relative abundance.

}, keywords = {LTER-KNZ}, doi = {10.1111/1365-2435.13135}, url = {https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2435.13135}, author = {Griffin-Nolan, Robert J. and Bushey, Julie A. and Carroll, Charles J. W. and Challis, Anthea and Chieppa, Jeff and Garbowski, Magda and Hoffman, Ava M. and Post, Alison K. and Slette, Ingrid J. and Spitzer, Daniel and Zambonini, Dario and Ocheltree, Troy W. and Tissue, David T. and Alan K. Knapp}, editor = {Fox, Charles} } @article {KNZ001823, title = {A safety vs efficiency trade-off identified in the hydraulic pathway of grass leaves is decoupled from photosynthesis, stomatal conductance and precipitation}, journal = {New Phytologist}, volume = {210}, year = {2016}, pages = {97-107}, abstract = {

A common theme in plant physiological research is the trade-off between stress tolerance and growth; an example of this trade-off at the tissue level is the safety vs efficiency hypothesis, which suggests that plants with the greatest resistance to hydraulic failure should have low maximum hydraulic conductance. Here, we quantified the leaf-level drought tolerance of nine C4 grasses as the leaf water potential at which plants lost 50\% (P50 \× RR ) of maximum leaf hydraulic conductance (Ksat ), and compared this trait with other leaf-level and whole-plant functions. We found a clear trade-off between Ksat and P50 \× RR when Ksat was normalized by leaf area and mass (P = 0.05 and 0.01, respectively). However, no trade-off existed between P50 \× RR and gas-exchange rates; rather, there was a positive relationship between P50 \× RR and photosynthesis (P = 0.08). P50 \× RR was not correlated with species distributions based on precipitation (P = 0.70), but was correlated with temperature during the wettest quarter of the year (P \< 0.01). These results suggest a trade-off between safety and efficiency in the hydraulic system of grass leaves, which can be decoupled from other leaf-level functions. The unique physiology of C4 plants and adaptations to pulse-driven systems may provide mechanisms that could decouple hydraulic conductance from other plant functions.

}, keywords = {LTER-KNZ}, doi = {http://dx.doi.org/10.1111/nph.13781}, url = {https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.13781}, author = {Ocheltree, Troy W. and Jesse B. Nippert and Prasad, P. V. Vara} }